Method of making mat type floor switches



June 9, 1964 L. A. WIKKERINK 3,136,333

METHOD OF MAKING MAT TYPE FLOOR SWITCHES Original Filed Nov. 26, 1957\KXKRK V// INVENTOR.

United States Patent 3,136,833 METHOD OF MAKING MAT TYPE FLOOR SWITCHESLance A. Wikkerink, Milwaukee, Wis., assignor to Republic Industries,Inc., Chicago, Ill., a corporation of Illinois Original application Nov.26, 1957, Ser. No. 699,07 6, now Patent No. 2,954,446, dated Sept. 27,1960. Divided and this application Dec. 2, 1959, Ser. No. 856,718

3 Claims. (Cl. 264-277) The present invention relates to molded mat typefloor switches and is a division of application Serial No. 699,076,filed November 26, 1957, now US. Patent No. 2,954,446.

Mat switches as contemplated by this invention are used for controllingthe operation of such devices as public building automatic door openers,for instance. They have much the appearance of a pliable floor mat, andthe molded resilient portion is usually formed of some pliable resin,such as a polyvinyl resin for instance.

In general, they consist of a bottommolded layer which is supported bythe floor and a top molded layer separated therefrom excepting that thelayers are joined at their edges. These two resilient layers enclose apair of metal sheets (aluminum is satisfactory) spaced slightly apart bya plurality of soft rubber buttons or the like. The two metal plates actas the contacts of an electric switch, and are held away from each otheruntil someone steps upon the mat, whereupon the two metal plates arepressed together locally so as to complete'an electrical circuit. Thisin turn, in any suitable fashion, controls the operation of an automaticdoor actuator.

One of the problems associated with such mats is that in order tofacilitate construction, and particularly to prevent water from seepinginto the interior, the top and bottom layers and the surrounding edge ofthe mat are molded in one operation so as to avoid the necessity forcemented seams. Although this molding operation is ordinarily conductedat low pressure, the polyvinyl resin, for instance, will, with any priorused sealing means I know of, flow inwardly between the aluminum sheetsat the spaced edges in an unpredictable fashion so that certain regionsof the sheets become permanently insulated from each other. These areasof the mat therefore be come insensitive to the weight of a personstepping thereon. For this reason, there is a considerable scrap loss inmats so produced.

Mats manufactured from precast cemented elements are even lesssatisfactory and therefore the practice has been to cast mats completein one operation and to accept the scrap loss as inevitable.

It is the principal object of my invention to provide an improved methodfor making a mat type floor switch of novel construction such that,although the top, bottom, and surrounding edge portion of the mat arecast as a single element so that no cemented seams are used, no seepageof the fluid plastics material takes place between the plates at theiredges in such fashion as to insulate certain regions of the plates fromeach other.

An additional object is to accomplish the above in such fashion thatalthough the fluid polyvinyl or other resin does not leak inwardlybetween the plates in an uncontrollable fashion, it nevertheless doesenter sufiiciently just at the edges to hermetically seal the plates toeach 7 other and to provide sufficient support and stiffness to preventthe possibility of the plates shifting relative to each other.

Still another object is to provide a method of making an improved mattype floor switch comprised of resilient top, bottom, and edge membersenclosing a pair of separated contact plates in which the plates arefirmly bonded to the resilient material at their edges as well as overtheir major external surface portions.

Yet another object is to provide a novel method for accomplishing theabove in a simple and straightforward fashion and at relatively lowcost, and such that there are substantially no unsatisfactory finishedmats produced which need to be rejected.

Gther objects and advantages will become apparent from the followingdescription of a preferred embodiment of my invention which isillustrated in the accompanying drawings.

In the drawings, in which similar characters of reference refer tosimilar parts throughout the several views,

FIG. 1 is a perspective view from above of a mat type floor switchproduced according to the teachings of the present invention;

FIG. 2 is a top view of a portion of the mat shown in FIG. 1, with thevarious layers thereof revealed by breaking away portions of the matstructure;

FIG. 3 may be considered as a vertical longitudinal sectional View takenin the direction of the arrows substantially along the line 3-3 of FIG.2;

FIG. 4 is an enlarged sectional view of a sub-assembly portion and maybe considered as being essentially a detail taken from FIG. 3; and

FIG. 5 is a sectional view similar to FIG. 3, but showing a minorvariation in the construction.

Referring to FIG. 1 of the drawings, the mat there shown may beconsidered as being representative of the type of article which formsthe subject matter of the present invention. Such mats are typically ofthe order of 45 inches long by 28 inches wide, although dimensions willvary according to preference. The main resilient mat portion isindicated by the numeral 10, this central area being usually surroundedby an extruded metal trim strip 12 which has a somewhat wider member 14at the threshold end interlocking with the resilient portion,'as shownin FIG. 3. This threshold is anchored to the floor so as to retain themat against shifting. The electrical leads 15 riveted to the contactplates also enter the mat at this end so as to be out of the way andprotected by the plate 14. Beneath the plate 14 they may turn downwardlyand pass through the floor if desired. Since the metal trim forms noportion of the present invention, it is shown in FIG. 1 only, exceptingfor the illustration of the previously mentioned interlocking feature inFIG. 3.

The top 16 and bottom 18 layers of the resilient polyvinyl material arejoined at their side and end edges 20 by the same material moldedintegrally therewith, all during one molding operation. The resilientmembers of the mat enclose a pair of spaced aluminum plates, the topplate being indicated by the numeral 22 and its bottom counterpart bythe numeral 24.

As shown in FIG. 3, the bottom plate 24 is indented locally from the topso as to form shallow circular recesses 26 at spaced intervalsthereover, and each of these recesses contains a soft rubber ring 28that extends above the top of its recess about of an inch or so. The topplate 22 rests upon the rubber rings 28 and is therefore spaced from thebottom sheet sufficiently to prevent electrical contact therebetween.

Around their aligned peripheral edges, plates 22 and 24 are separated bya strip 30 of cotton webbing. This webbing, as shown, is approximatelyof an inch thick so as to maintain the plate spacing, and has a width ofabout /8 of an inch or so. This element 30 may be manufactured of any ofseveral materials which will suggest themselves; the importantconsideration being that .it be porous or bibulous and have considerablecapillary attraction for the polyvinyl or similar material when thismaterial is in the liquid state. It should also have sulficientresistance to compression and extrusion so as to maintain its thicknessdimension reasonably well under the pressure conditions prevailingduring the molding operation.

The edges of the plates are enclosed and the external faces near theedges embraced by a U-shaped strip of extruded vinyl plastic materialindicated at 32. This channel strip extends entirely around theperiphery of the plates so that substantially no portion of the plateedges is exposed.

The mat may be manufactured or assembled as follows: The bottom plate24, with its electric lead 15 riveted thereto in the usual fashion, isset upon an approximately level surface and the resilient rings 28located so that one of these is in each of the depressions 26. Tofacilitate handling, these rings may be lightly secured in position bycementing. Thereafter the strip of webbing 30 is secured by any suitableadhesive to the upper surface of the plate 24, with the outer edge ofthe webbing approximately flush with the edge of the plate. The topplate 22, with its lead 15 secured thereto, is then put into position,and the extruded vinyl channel strip 32 is pressed over the edges of theplates all the way around so as to secure the assembly together so thatit can be handled as a unit.

The mold, which may be conventional, is then opened, and a plurality ofpolyvinyl blocks-one of which is shown at 34 in FIG. 4are located in thebottom of the mold. These blocks have a height equivalent to thedistance between the bottom of the plate 24 and the bottom of the mat.Their purpose is to support the previously described plate assembly inposition centered with respect to the top and bottom of the mold so asto permit the liquid vinyl material to flow underneath the plate 24 toform the mat bottom member 18.

The mold is then closed in the usual fashion, and the fluid polyvinylmaterial injected so as to fill all the space within the mold cavity.

The liquid polyvinyl material will act partially to soften the blocks 34and incorporate them in the fluid mass sufiiciently so that they becomean integral part thereof. Since they do not have time to soften all theway through, however, they maintain the spacing of the plate 24 abovethe bottom surface of the mat during setting of the molded article. Inaddition to filling the mold space, the liquid polyvinyl material alsosoftens the channel strip 32 somewhat so as to incorporate this in thefluid mass, and some of the liquid material will leak between theexternal faces of the plates 22 and 24 and the overlying arms of thechannel member 32 and will tend to flow between the plates 22 and 24 attheir edges. This liquid material is, however, absorbed by the webbing30 with the result that a considerable portion of this webbing towardthe peripheral edges of the plates becomes saturated with the vinylmaterial and therefore bonds the plates and webbing firmly together. Thevinyl material, however, does not soak all the way through the webbingat any point so as to flow beyond the inner edge thereof. Instead, anyexcess vinyl material, due to a comparatively large order of leakage atsome particular spot, will spread longitudinally because of thecapillary attraction of the fibrous mass at 30.

Thus, the top and bottom resilient portions 16 and 18 of the mat,together with the edge and end portions 20, are formed as one unitarycasting, with the electrical leads embedded and sealed therein, and thesupport blocks 34 and channel members 32 are incorporated as a portionof the cast material. Furthermore, the cast material also saturatesportions of the fibrous mass 30. The result is that the plates 22 and 24are completely enclosed and bonded both to the top and bottom resilientmembers 16 and 18 as well as to each other around their edges. The metaledges therefore cannot work or shift slightly so as to cut the matmaterial. The mat therefore is completely waterproof and has a greaterlife in service than other mats of this general character with which Iam familiar. Also, as pointed out previously, rejections because ofdefective mats are cut to a minimum.

The arrangement of FIG. 5 shows a somewhat simpler construction in thatit is not necessary to shape the lower sheet 24 so as to form thedepressions or pockets 26. In PEG. 5 both of the sheets 22 and 24 areflat and are spaced apart by rubber rings or buttons 28 which differfrom the rings 28 in that they are somewhat thinner. Theoretically, amat as thus constructed might be considered to be insensitive if, instepping upon the mat, all of the weight were centered over one of thebuttons 28. However, the flexibility of the upper surface portion 16 issufficient so that as a practical result some portion of the plates 22and 24' will be brought together in the immediate vicinity of the button28. In general, the construction illustrated in FIG. 5 is less expensiveand has proved to be satisfactory in service. The construction of FIG.3, although it involves an additional operation, is preferred,principally because the rings 28 are never compressed to less thanapproximately half of their height, and therefore the service life ofthe mat of FIG. 3 is somewhat greater than that of the mat illustratedin FIG. 5.

In the above description of a preferred embodiment of the inventioncertain dimensions and specific materials have been recited in theinterest of clarity of understanding. It will be understood, however,that alterations and substitutions can be made without departing fromthe scope or spirit of the invention, and that the scope of theinvention is to be measured by the scope of the following claims.

Having described my invention, what I claim as new and useful and desireto secure by Letters Patent of the United States is:

1. The process of making pedestrian weight-operated mat switches of thetype in which a pair of large area switch plates are spaced apart andencapsulated within a plastic substance which has a resilient elastomerstate which adheres to metal surfaces when cured and a liquid stateprior to curing; which comprises stacking a pair of aligned flexiblemetal plates of substantially identical size and shape spaced slightlyapart at their edges all the way around the peripheries of said platesby an intervening narrow barrier strip; said barrier strip beingresistant to compression and extrusion and formed of a pliable,bibulous, electrically insulating material which has a high degree ofabsorbency for the liquid plastic substance, and which is substantiallyunalfected by the liquid plastic substance or the curing step for saidplastic substance; forming a subassembly by lightly clamping the plateedges against the intervening barrier strip by pressing a channel stripover the edges of said plates so as to enclose and partially seal theplate edges to provide limited liquid access to the barrier stripexternal edge, supporting said subassembly in a mold cavity providingclearance around said subassembly, filling said cavity with the plasticsubstance in the liquid state so as to submerge the plates and channelstrip within the liquid plastic mass, a minor portion of the liquidplastic substance in the mold seeping through the partial seal betweenthe channel strip and the plate edges and being absorbed by the bibulousbarrier strip, and subsequently curing all of the liquid plasticsubstance together to the resilient state, the absorbed plastic materialafter curing acting to bond the plates to each other and to the barrierstrip, whereby in the cured assembly the plates are spaced apart andsecured together at and near their edges by the plastic substancereinforced by the barrier strip substance and the plates are completelyenclosed within the mass of plastic substance in the resilient elastomerstate.

2. The method called for in claim 1 in which the barrier strip hassubstantially the characteristics of cotton webbing.

3. The method called for in claim 1 in which the channel strip is formedof substantially the same material as the resilient encapsulatingplastic substance.

References Cited in the file of this patent UNITED STATES PATENTS2,251,351 Cooper Aug. 5, 1941 2,346,640 Anthony Apr. 18, 1944 2,466,586Evans Apr. 5, 1949 2,604,661 Karns July 29, 1952 2,940,127 Schils June14, 1960 FOREIGN PATENTS 657,821 Great Britain Sept. 26, 1951

1. THE PROCESS OF MAKING PRDESTRAN WEIGHT-OPERATED MAT SWITCHES OF THETYPE IN WHICH A PAIR OF LARGE AREA SWITCH PLATES ARE SPACED APART ANDENCAPSULATED WITHIN A PLASTIC SUBSTANCE WHICH HAS A RESILIENT ELASTOMERSTATE WHICH ADHERES TO METAL SURFACES WHEN CURED AND A LIQUID STATEPRIOR TO CURING; WHICH COMPRISES STACKING A PAIR OF ALIGNED FLEXIBLEMETAL PLATES OF SUBSTATIALLY IDENTICAL SIZE AND SHAPE SPACED SLIGHTLYAPART AT THEIR EDGES ALL THE WAY AROUND THE PERIPHERIES OF SAID PLATESBY AN INTERVENING NARROW BARRIER STRIP; SAID BARRIER STRIP BEINGRESISTANT TO COMPRESSION AND EXTRUSION AND FORMED OF A PLIABLE,BIBULOUS, ELECTRICALY INSLATING MATERIAL WHICH HAS A HIGH DEGREE OFABSORBENCY FOR THE LIQUID PLASTIC SUBSTANCE, AND WHICH IS SUBSTANTIALLYUNAFFECTED BY THE LIQUID PLASTIC SUBSTANCE OR THE CURING STEP FOR SAIDPLASTIC SUBSTANCE; FORMING A SUBASSEMBLY BY LIGHTLY CLAMPING THE PLATEEDGES AGAINST THE INTERVENING BARRIER STRIP BY PRESSING A CHNNEL STRIPOVER THE EDGES OF SAID PLATES SO AS TO ENCLOSE AND PARTIALLY SEAL THEPLATE EDGES TO PROVIDE LIMITED LIQUID ACCESS TO THE BARRIER STRIPEXTERNAL EDGE, SUPPORTING SAID SUBASSEMBLY IN A MOLD CAVITY PROVIDINGCLEARANCE AROUND SAID SUBASSEMBLY, FILLING SAID CAVITY WITH THE PLASTICSUBSTANCE INTHE LIQUID STATE SO AS TO SUBMERGE THE PLATES AND CHANNELSTRIP WITHIN THE LIQUID PLASTIC MASS, A MINOR PORTION OF THE LIQUIDPLASTIC SUBSTANCE IN THE MOLD SEEPING THROUGH THE PARTIAL SEAL BETWEENTHE CHANNEL STRIP AND THE PLATE EDGES AND BEING ABSORBED BY THE BIBULOUSBARRIER STRIP, AND SUBSEQUENTLY CURINGALL OF HTE LIQUID PLASTICSUBSTANCE TOGETHER TO THE RESILIENT STATE, THE ABSORBED PLASTIC MATERIALAFTER CURING ACTING TO BOND THE PLASTE TO EACH OTHER AND TO THE BARRIERSTRIP, WHEREBY IN THE CURED ASSEMBLY THE PLATES ARE SPACED APART ANDSECURED TOGETHER AT AND NEAR THEIR EDGES BY THE PLASTIC SUBSTANCEREINFORCED BY THE BARRIER STRIP SUBSTANCE AND THE PLATES ARE COMPLETELYENCLOSE WITHIN THE MASS OF PLASTIC SUBSTANCE IN THE RESILIENT ELASTOMERSTATE.